Ridge

Ridge

The ridge is a distinctive line of hair along a dog’s spine that grows in the opposite direction from the rest of the coat. It is a key feature of Rhodesian Ridgeback and the Thai Ridgeback. The ridge typically measures 2 to 5 cm at its widest point and tapers toward the tail. Hair follicles in the ridge grow in the opposite direction compared to those in dogs without a ridge.

Genetically, the ridge is caused by a large duplication on chromosome 18, which includes the genes FGF3, FGF4, FGF19, and ORAOV1. Fibroblast growth factor (FGF) genes encode signalling proteins that play key roles in cell growth, development, tissue repair, and metabolism, including hair follicle morphogenesis. The role of ORAOV1 in dogs is not yet fully understood.

Dermoid sinus

Dogs that carry two copies of the ridge allele (homozygous) have a slightly increased risk of developing dermoid sinus (DS), although the link is not very strong. DS is a congenital condition in which a tube-like tract forms under the skin along the spine. This tract can lead to infections, abscesses, or neurological problems.

Inheritance

The ridge is inherited as an autosomal dominant trait with incomplete penetrance, which means that not all dogs carrying the ridge allele will display the ridge.

• Heterozygous dogs (R/r) usually show the ridge, with about 95% expressing the trait. In roughly 5%, the dominant allele is suppressed, and the ridge does not appear.
• Homozygous dogs (R/R) always have the ridge.
• Dogs without the allele (r/r) do not develop a ridge.

Relevant Tests

• H944